This invention relates to the shaping of heat-softened glass sheets or the like by pressing the sheets between rigid pressing members of complementary curvature. This technique, known as press bending, lends itself to relatively inexpensive mass production of bent glass sheets within precise tolerances.
A particularly advantageous press bending apparatus is disclosed in U.S. Pat. No. 3,367,764 to S. L. Seymour. A feature of that patented apparatus is the provision of a relatively flexible shaping plate of adjustable curvature adjustably attached to a relatively rigid plate, so as to enable adjustments to the curvature of the shaping plate to be made simply and quickly. Adjustments are made possible by the use of a large number of threaded rods and nuts to attach the shaping plate to the rigid plate. By turning the nuts, the distance between a portion of the shaping plate and the rigid plate can be changed. While such an arrangement possesses many advantages, it would be desirable to reduce the time required to carry out the many adjustments needed to conform the curvature of the shaping plate to a given standard.
The flexible shaping plate can be more quickly and accurately adjusted by affixing the shaping plate to a rigid adjusting plate made up of a plurality of segments, as is shown and described in U.S. Pat. application Ser. No. 745,909 of Samuel L. Seymour, filed Nov. 29, 1976, now U.S. Pat. No. 4,052,188. Each segment of the adjusting plate carries a plurality of adjustable connectors which join the segment with a portion of the shaping plate. Each adjusting plate segment, in turn, is adjutably mounted onto a rigid back plate. Thus, small, localized changes in the shaping plate curvature may be made by adjusting the distance between points on the shaping plate and the adjusting plate by means of individual connectors, while major adjustments involving an entire zone of the shaping plate as a whole are carried out by reorienting one or more of the adjusting plate sections. By this arrangement, an overall curvature correction can be effected without disturbing each individual adjusting connector. For example, in a case where it is desired to slightly flatten the curvature of a compound curve in one direction only, the provision of sectionalized adjusting plates permits the adjustment to be carried out without disrupting the curvature in the other direction. The adjusting plate segments, although relatively rigid, can be flexed to some degree, which provides a second advantageous mode of adjustment. By slightly flexing one of the adjusting plate segments, the overall curvature of one region of the shaping plate can be smoothly altered without disrupting the curvature of the remainder of the shaping plate.
Notwithstanding the aforesaid enumerated inventions, shaping plates of adjustable curvature tended to depart from their desired shape with time as repeated, intermittent use in a mass production operation and mishandling during conveyance between an operating line and a storage area caused deviations from desired curvature of the shaping plates. Furthermore, these deviations from curvature seemed to occur with more frequency in shaping plates of press bending apparatus for fabricating relatively simple bends, that is, those of relatively simple cylindrical curvatures. These deviations from curvature were most frequently found in the vicinity of notched portions in the shaping plates. Such notched portions are needed along the upper edge of the shaping plates to provide clearances to receive the glass engaging elements of self-closing tongs from which glass sheets are suspended during a press bending operation.